StringBuffer StringBuffer is mutable means one can change the value of the object . The object created through StringBuffer is stored in the heap. StringBuffer has the same methods as the StringBuilder , but each method in StringBuffer is synchronized that is StringBuffer is thread safe . Due to this it does not allow two threads to simultaneously access the same method . Each method can be accessed by one thread at a time . But being thread safe has disadvantages too as the performance of the StringBuffer hits due to thread safe property . Thus StringBuilder is faster than the StringBuffer when calling the same methods of each class. String Buffer can be converted to the string by using toString() method. StringBuffer demo1 = new StringBuffer("Hello") ; // The above object stored in heap and its value can be changed . demo1=new StringBuffer("Bye"); // Above statement is right as it modifies the value which is allowed in the StringBuffer StringBuilder StringBuilder is same as the StringBuffer , that is it stores the object in heap and it can also be modified . The main difference between the StringBuffer and StringBuilder is that StringBuilder is also not thread safe. StringBuilder is fast as it is not thread safe . StringBuilder demo2= new StringBuilder("Hello"); // The above object too is stored in the heap and its value can be modified demo2=new StringBuilder("Bye"); // Above statement is right as it modifies the value which is allowed in the StringBuilder